Medic leapfrogs it in muck (4)
I believe the answer is:
dirt
'muck' is the definition.
(I've seen this before)
'medic leapfrogs it' is the wordplay.
'medic leapfrogs' becomes 'dir' (I can't justify this - if you can you should believe this answer much more).
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'dir'+'t'='DIRT'
'in' is the link.
Can you help me to learn more?
(Other definitions for dirt that I've seen before include "Scandalous information" , "Muck" , "scandalous gossip" , "Earth; grime" , "Loose soil; filth" .)